1. Field of the Invention
The present invention relates to a variable capacitance component.
2. Description of the Related Art
A variable capacitance component is known that has a capacitance varied by changing a permittivity of a dielectric layer by an applied voltage.
For example, Japanese Laid-Open Patent Publication No. 2011-101041 discloses a variable capacitance component having dielectric layers and electrodes alternately laminated so that the electrodes are formed into a comb shape.
WO 2013/061985 discloses a variable capacitance component in which ferroelectric thin films and film electrodes are respectively formed by a chemical solution deposition (CSD) method and a sputtering method.
A variable capacitance component having electrodes formed into a comb shape as described in Japanese Laid-Open Patent Publication No. 2011-101041 has a stray capacitance increased due to an electrode structure thereof and it is not easy to make a capacitance variable rate larger. Comb-shaped electrodes have portions (extending portions) extending from overlapping portions of electrodes facing each other toward respective opposite end surfaces. The present inventor discovered that such a structure generates a stray capacitance between the overlapping portions and the extending portions of the electrodes and that if the capacitance is reduced by making an overlapping area of the electrodes smaller or by making an applied voltage larger, the effect of this stray capacitance becomes relatively large and the capacitance variable rate decreases.
The variable capacitance component as described above has a dielectric layer and an electrode layer laminated and sintered at the same time. Therefore, it is generally difficult to use a low-loss metal such as Ag and Cu having a low melting point. To use such a metal, a sintering additive such as glass must be added to the dielectric layer to perform low-temperature firing. As a result, the performance of the dielectric layer is sacrificed.
An element obtained by the method of WO 2013/061985 has a relatively large conduction loss because a skin depth cannot be satisfied due to a thin thickness of electrodes and because an electrode material is limited to Pt or Au etc., so as to prevent peeling during annealing treatment after electrode formation and it is difficult to use Ag or Cu having a low loss at high frequency. Additionally, it is known that, if the CSD (chemical solution deposition) method or the sputtering method of WO 2013/061985 is used in order to increase the thickness of electrodes, a hillock is formed after the thickness exceeds about 500 nm, which may lead to a failure in a subsequent manufacturing process such as a lamination process. Although it is important to give consideration to impedance matching for reducing a loss in a device used at high frequency, the impedance matching is not easy in the method described in WO 2013/061985.